Motor-operated rotary input tap selector switch to regulate line voltage in x-ray system



Sept 23, 1969 R I T, ET AL 3,469,100

METHOD-OPERATED ROTARY INPUT TAP SELECTOR SWITCH To REGULATE LINEVOLTAGE IN X-RAY SYSTEM Filed Feb 16, 1967 INVENTORS RoberTL.Wrigh'r,dr. 8 William N. Sweet. BY

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' AGENT WITNESSES Iot m mmwoEP Om United States Patent MUTflR-GPERATEDROTARY INPUT TAP SELEC- TUR SWITCH TO REGULATE LINE VOLTAGE IN X-RAYSYSTEM Robert L. Wright, .lr., North Linthicum, and William N.

Sweet, Baltimore, Md, assignors to Westinghouse Electrie Corporation,Pittsburgh, Pin, a corporation of Pennsylvania Filed Feb. 16, 1967, Ser.1 0. 616,696 Int. Cl. HOSg N32 ABSTRACT OF THE DISCLOSURE Amotor-operated rotary input tap selector switch selects, via contactbars, the proper input winding turns of the auto-transformer to maintainoutput nearly constant in spite of variation in line voltage. Areversible motor for the switch is controlled via relays by a pair ofthyratron tubes according to such line voltage variation, and a chokemeans connected to a pair of supply line input brushes in the rotaryswitch generates a bias signal at the thyratron tubes which prevents themotor from stopping such brushes when as a pair they are bridging twocontact bars, while at the same time preventing excessive current flowthrough the momentarily shorted turn of the autotransformer establishedby such bridging. An interlock relay controlled by thethyratron-controlled relays prevents the motor from being started duringan X-ray exposure and prevents such an exposure from being initiatedwhile the motor is operating.

Background of the invention (1) The field of art to which the presentinvention pertains is X-ray electrical systems which operate from an AC.supply line, and more particularly to such systems as include linevoltage regulating apparatus therein.

(2) Line voltage regulating apparatus in X-ray electrical systemsheretofore have included a manually-operated selector switch havingfixed contact bars connected to different supply line input windingturns of the autotransformer from which the system is fed and a pair ofcontact brushes connected to one side of the supply line and movable inunison for mutual contact with a selected fixed contact bar. The twocontact brushes have been so dimensioned and spaced-apart that at leastone of the two is always in engagement with a fixed contact bar toprevent deenergization of the autotransformer during operation of theregulator switch. This results in bridging of two adjacent fixed contactbars from one brush to the other while being transferred to a selectednew position. Such bridging tends to short circuit the transformerwinding connected at opposite ends to the two bridged contact bars. Asmall resistor has been interposed between the brushes to reduce currentflow through such winding under the bridged condition, and a mechanicaldetent means has been employed to urge the brushes to pass rapidly fromone position to another and to hold any such position which may beselected. The resistor is adequate to take care of the usual momentarybridging conditions of the brushes while in transit between stoppositions; however, it occasionally happens that the brushes get hung upin a midposition which results in burn-out of the resistor or of therespective transformer winding short-circuited by such resistor.Accordingly, it

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becomes a prime object of the present invention to provide line voltageregulator apparatus which automatically repositions the selector switchbrushes according to line voltage variation while preventing suchbrushes from coming to rest in a bridging position across two contactbars of such switch.

Summary In accord with general features of the present invention, theabove object is obtained by provision of a reversible motor foroperating the pair of contact brushes of the input tap selector switch;relay means controlling operation of said motor respousively to linevoltage variation; means sensitive to voltage conditions across thebrushes for preventing dropout of said relay means when the pair ofbrushes is bridging adjacent contact bars in the selector switch; andmeans for preventing operation of the switch-operating motor during theeffecting of an X-ray exposure, and for preventing an X-ray exposurewhile such motor is being operated.

Brief description of the drawing The single figure is a circuit diagramof an illustrative embodiment of the invention.

Description of preferred embodiment Assuming the line switch S to beclosed, the autotransformer T for the X-ray system has taps A and Anominally at volts. Output from A A is rectified by CR and appears asnominally 170 volts DC. on a capacitor C Discharging this capacitor aretwo paths, a reference path consisting of R reference tube V andresistor R an action network comprising resistors R 4 6, 2, 3 and 11-The reference tube V is a constant voltage tube so that in the referencepath such tube has a constant voltage drop across it. R has a smallvalue, and unless other currents are fed through it, as hereinafter setforth, has no significant effect. The anode of reference tube V will beat a constant value of 108 volts, for example, irrespective of the usualline voltage variations.

The R resistor of the action network drops C voltage to 118 volts at theR terminal. The arm of R, is connected to the cathode of a thyratrontube V of a first relay means; the control grid of V being connected tothe reference anode of tube V The R, arm is adjusted so that normallythe voltage at the V cathode is sufiiciently above that at the V controlgrid that tube V is not conductive; cathode at 111 volts and controlgrid at 108 volts, for example. If the line voltage falls, the 170 voltsnominal at capacitor C drops, say to 168 volts, for example, and the Vcathode voltage drops correspondingly to such as 110 volts to cause tubeV to fire; a transformer T having its primary connected across A -A andits secondary connected across the tube V establishes an AC. platevoltage across tube V of such as volts, for example, in series with thewinding of a relay K The other part of the action network includesresistors R and R7. The arm of R is connected to the control grid of asecond thyratron tube V of a second relay means; the cathode of V beingconnected to the V reference. R is adjusted so that at nominal linevoltage V does not fire, but if the C voltage rises in consequence of anincrease in such line voltage, V grid voltage becomes more positive andV is caused to fire. A transformer T similar to T provides plate voltagefor tube V and the coil of a relay K is in series with such tube.

During any period of conductance of either thyratron tube V or V eachfires on one-half cycle of the A.C. wave and extinguishes on thealternate half cycle. Rectifiers CR and CR in parallel with the coils ofrelays K and K respectively, hold such relays picked-up for a half-cycleperiod following conductance of the tubes V and V respectively.

From the foregoing it will be understood that V fires successively topick up relay K when the line voltage as represented at A -A is too low,and V fires successively to pick up the relay K when the line voltage istoo high. When picked up, the relay K or K opens its 5, 8 contacts todisrupt an X-ray exposure control lead C and deenergize relay K and openits contacts 1, 2 to prevent the energizing of the primary of highvoltage transformer T and thus the effecting of an X-ray exposure whilethe line voltage regulator apparatus is in operation. At the same time,the pick-up relay K or K closes its contacts 8, 6 to short theappropriate shading coil 25 or 26 of the selector-switch-driving motorMD, for turning the brushes 30 of the rotary selector switch S in theappropriate direction for switching to a contact bar 32, 33, 34, henceinput tap 42, 43, 44 to the autotransformer T suited to the A.C. supplyline voltage; 212 volts, 208 volts, 204 volts, etc., for example.

At the same time, 1, 3 contacts are closed by the pickedup one of therelays K K to establish via CR a rectified voltage, six volts forexample, from an isolated detector winding 46 of a choke 48 afliliatedwith the brushes of switch S and applies this voltage to R or Raccording to which of such relays is picked up. Such voltage to R or Ris of such a value and polarity that V or V will have an overwhelmingsignal to continue to conduct during every other half-cycle period. Aswill be apparent hereinafter, the detector winding 46 produces suchholding signal exclusively while the' pair of brushes of switch Sbridges two adjacent contact bars to assure that the switch-drivingmotor will not stop during such bridging.

Upon establishment of the nominal voltage at A -A of the autotransformerT commensurate with selection of the proper input tap suited to theexisting line voltage, and in the absence of a signal from the detectorwinding 46, the respective one of the tubes V and V will cease itsperiodic firing and its respective relay K or K will drop out to openits contacts 1, 3 and 6, 8 and close its contacts 5, 8 to energize relayK, from an XP tap on the autotransformer by way of a trigger switch 50and the 1, 2 contacts of an interlock relay K energized initially viasuch trigger switch, the contacts 5, 8 of relay K and the lead 0,, andthereafter by way of such trigger switch and such contacts 1, 2 as ahold circuit independent of the K relay. At the same time, the relay Kwhen picked up, opens contacts 3, 4 in the energizing circuit for thearmature of the drive motor MD, to prevent operation of the rotaryselector switch 5, while an X-ray exposure is being effected viacontacts 1, 2 of the K relay.

By way of further detail of construction and operation of theillustrative embodiment, the two movable contacts, or brushes, of therotary selector switch S are mechanically coupled for movement in unisonby the armature of drive motor MD, and are connected as a pair across awinding 52 of the aforementioned choke 48, which winding has a centertap connected to one side of the AC. supply line via line switch S Whenthe pair of contacts are connected across the adjacent contact barsmomentarily during actuation by the motor MD,, the centertapped chokecoil presents sufiicient reactance to limit current through themomentarily shorted turn of the autotransformer T to a safe value. Whenthe centertapped choke coil 52 is connected at its opposite ends to thesame contact bar, it is short-circuited and its two halves cancel outeach other, its impedance is near zero and the volts per turn of theturns of such coil are near zero. When the brushes are bridging thecontact bars, the volts per turn of the center-tapped choke coil 52therebetween is high. The detector winding 46 is electromagneticallycoupled to the center-tapped coil 52 of the choke 48 so that it developsa voltage correspondingly and creates the aforedescribed hold signalexclusively when theswitch S brushes are bridging the contact bars.

In the circuit diagram shown in the drawing, the thyratron tubes V and Vhave been exemplified as types 2D21 and the values of circuit componentsgiven in the drawing are aimed at compatability with such particulartubes. The description of the exemplified embodiment of the inventionhas been limited to that required for a basic understanding of theoperation of such embodiment; for other minor structural details resortmay be had to such circuit diagram.

We claim as our invention:

1. In an X-ray system operated from an AC. supply line to produce X-rayexposures comprising an autotransformer from which electrical energy foroperating components of the system is derived and which has multiplesupply line input taps; and an input tap selector switch havingspaced-apart contact bars electrically connected to respective ones ofsaid input taps and having a pair of supply line input tap-selectorbrushes movable in unison for mutual engagement exclusively with aselected contact bar, which brushes are so proportioned and arrangedthat during transit at least one brush is in engagement with a contactbar at all times, no single one of such brushes will bridge two adjacentcontact bars, but such adjacent contact bars become bridged by suchbrushes as a pair;

wherein the improvement comprises:

a reversible drive motor for actuating said pair of brushes,

relay means for effecting start-stop operation of said motor in oppositedirections,

a control means for controlling operation of said relay meansresponsively to variation in supply line voltage, and

an interlock means sensitive to a voltage difference between saidbrushes for preventing said control means from operating said relaymeans to stop said motor when said pair of line input brushes isbridging two contact bars.

2. The X-ray system of claim 1, wherein:

said control means comprises:

a pair of thyratron tubes,

a bias control means for said thyratron tubes for establishing biassignals proportionate to variation in line voltage relative to a stablereference voltage, and

circuit means for impressing alternating voltages from anode-to-cathodeacross said tubes, whereby, in the presence of the proper control bias,such tubes conduct and extinguish during each complete cycle of suchalternating voltage; and

said relay means includes two relay coils in series with said thyratrontubes, respectively, and rectifiers in parallel with said coils torevent relay dropout between two consecutive periods of thyratronhalf-cycle conduction.

3. The X-ray system of claim 2 wherein:

said interlock means forms a part of said bias control means for thethyratron tubes and includes a detector winding electromagneticallycoupled to a centertapped choke winding connected at its opposite endsto the aforesaid brushes and at its center to one side of a supply inputline to the system, whereby a tube conduction assuring bias signal isgenerated in such detector winding while said pair of brushes bridgesadjacent contact bars which overrides anyline-voltage-variation-developed bias signal.

4. The X-ray system of claim 2, wherein: the line-voltage-variation biassignals are impressed from cathode to screen on one thyratron tube andreversely on the other thyratron tube, whereby one tube Will conductupon an increase in supply line voltage above a datum value and theother Will conduct upon a decrease. 5. The X-ray system of claim 1,further comprising a second relay means responsive to said control meansfor preventing X-ray exposure operation of such system dur- 1O ingactuation of the tap-selector brushes.

References Cited UNITED STATES PATENTS 3/1962 Boldingh 250-103 5/1966Conner 323-435 US. Cl. X.R. 323-435

